Let's solve this addition problem. We have 2868080368 and 7800420997, and we need to add them together.

Step 1: We'll start by adding the digits 8 & 7 in column 1 and get 15.
We'll write down the last digit 5 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 6 & 9 in column 2 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 3 & 9 in column 3 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 0 & 0 in column 4 and get 1.

Step 5: We'll start by adding the digits 8 & 2 in column 5 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

Step 6: We'll start by adding the digits 0 & 4 in column 6 and get 5.

Step 7: We'll start by adding the digits 8 & 0 in column 7 and get 8.

Step 8: We'll start by adding the digits 6 & 0 in column 8 and get 6.

Step 9: We'll start by adding the digits 8 & 8 in column 9 and get 16.
We'll write down the last digit 6 and carry the 1 to the next column.

Step 10: We'll start by adding the digits 2 & 7 in column 10 and get 10.
We'll write down the last digit 0 and carry the 1 to the next column.

So, 2868080368 + 7800420997 = 10668501365.

